One of important roles of a sensor is detecting various chemicals or materials originating from living creatures, such as concentration of a variety of ions, concentration of gases such as oxygen or carbon dioxide and the like. In order to monitor water pollution, air pollution and the like which may occur in our surrounding environment, sensors capable of measuring various gases such as CO, COx and the like, ions and humidity are frequently used. In the case of gas sensors, numerous sensors haven been developed starting from the catalytic combustion type sensor of Johnson introduced in 1923. In the case of semiconductor gas sensors, they can be largely divided into resistive type sensors and non-resistive type sensors, and the semiconductor gas sensor is a very useful since it may detect various kinds of gases.
As high-tech elements with superior performance have been developed using a material such as polymer, semiconductor, ceramic or the like, humidity sensors are also developed in the form of converting humidity into electric signals and, specifically, a sensor for converting humidity and outputting impedance, electrical conductivity, thermal conductance, electrostatic capacitance or the like.
A method of measuring humidity is divided into a direct measurement method and an indirect measurement method. The direct measurement method includes various hygrometers based on a saturation, absorption or evaporation method. The indirect measurement method includes a method of evaluating moisture adsorption or spectroscopic characteristics, and measurements of electrical conductivity, surface conductivity, change of dielectric constant, near infrared absorption, pressure difference by diffusion speed, change of ionization potential and the like correspond thereto.
Although LEDs are widely used in the present and gradually extending their application fields in a specific area related to illumination, a function as a sensor is performed by individual sensors irrelevant to the LEDs as described above. Accordingly, a sensor formed in a structure integrated with an LED cannot be found in the prior art, and, particularly, an LED sensor for measuring a specific pollutant or measuring temperature or pressure in such a structure and informing a degree of pollution does not exist now.